My question applies to the client (laptop) side. In a worst case scenario, the analog line into your terminal server, router modem, etc. is all you have (primary network down). If I don't have access (at the laptop side) to an analog circuit (POTS), is there another way: i.e. AirCard, Cell Phone, etc. to get my laptop connected to analog modem at other end?

For applications with many, small remote sites, hanging a modem off the router is a very cost effective OOB solution. I'm trying to find an alternative to always having an analog circuit (POTS) connected to my laptop.

Along with the Avocent devices we use their DSView software. We can connect to the server running DSView (RDP, HTTPS, etc) and we can tell the server to connect to the router via IP or if the WAN link is down via a dial-up connection. We can now see and control the dial-up session between the DSView server and the router. The DSView server basically acts as a modem proxy, which is what I think you're looking for.

HTH